Why do Indexed Views not permit non-unique clustered indexes?

Question

I've been looking into using Indexed Views to increase performance on a few of our most commonly used views.

However Indexed Views do not support non-unique clustered indexes which goes a little against the precedence set by the rest of the database structure.

For example, here is a simplified version of a couple of our tables.

-Groups-
Group ID    GroupName

-Users-
UserKey    UserName    FullName     GroupID

The indexes are on Groups.GroupID (Non-clustered) and Users.GroupID (Clustered). The clustered key being on GroupID in the Users table as most commonly a range of users from a specific group would be retrieved. Obviously you would have multiple users per group, so this clustered index is non-unique.

This leaves me a bit uncertain of how to follow this precedence when indexing my views such as this example, as I cannot have a non-unique clustered index.

ConsumableID    ConsumableVariantID AllowThresholdOverwrite FullPath    GroupID ManufacturerID  Type    ModelID
101              29                 1                       0.1.2.4.    4       3               3       2

In actuality the only value on this View which would always be unique is the ConsumableID column, so I am left with little choice as of where to place my index.

Why do Views not permit non-unique clustered indexes when regular tables do?